Spinal Cord and Spinal
Nerves
Spinal Cord
• Enclosed in the vertebral canal, extends
from the foramen magnum of the skull to
the first or second lumbar vertebra where
it terminates in the cone shaped conus
medullaris
Spinal Cord
• Spinal meninges;
Dura Mater – outer
Arachnoid Mater – middle
Pia Mater – inner
Spinal Cord
• Dura Mater – composed of dense,
irregular connective tissue
Spinal Cord
• Arachnoid Mater – It is an avascular
covering with a spider’s web arrangement
of delicate collagen fibers and some
elastic fibers
Spinal Cord
• Pia Mater – A vascular and thin
transparent connective tissue layer
composed of interlacing bundles of
collagen fibers and some fine elastic fibers
Spinal Cord
• Subarachnoid space – between the
arachnoid mater and pia mater which
contains cerebrospinal fluid
Spinal Cord
The dura mater and arachnoid meningeal
coverings extend beyond the conus
medullaris, approximately to the level of
S2
Spinal Cord
• Filium terminale – a fibrous extension of
the pia mater, extends farther and
attaches to the posterior coccyx
Spinal Cord
• 31 pairs of spinal nerves, which exit via
the intervertebral foramina
Spinal Cord
• Since the spinal cord doesn’t extend to the
end of the vertebral column, the spinal
nerves emerging from the inferior end
must travel through the vertebral canal
until reaching the appropriate
intervertebral foramina
Spinal Cord
• This collection of spinal nerves are called
the cauda equina
Spinal Cord / Gray Matter
• Looks like an H
Spinal Cord / Gray Matter
• Posterior or dorsal horns – posterior
projections
Spinal Cord / Gray Matter
• Anterior or ventral horns – anterior
projections that contain cell bodies of
motor neurons
Spinal Cord / Gray Matter
• Lateral Horns – In the thoracic and lumbar
regions there is a lateral outpocketing of
gray matter
Spinal Cord / Gray Matter
• Gray commissure – central area of gray
matter
Spinal Cord / Gray Matter
• Dorsal root – Sensory fibers enter the cord
here
Spinal Cord / Gray Matter
• Dorsal Root Ganglia – Cell bodies of
sensory neurons located here
Spinal Cord / Gray Matter
• Ventral Roots – Motor neurons leave the
cord here
Spinal Cord / Gray Matter
• Spinal nerves – are formed from the fusion
of the dorsal and ventral roots
Spinal Cord / Gray Matter
Spinal Nerves;
8 pairs of cervical nerves
12 pairs of thoracic nerves
5 pairs of lumbar nerves
5 pairs of sacral nerves
1 pair of coccygeal nerves
Spinal Cord / White Matter
• The anterior median fissure and the
posterior median sulcus divide the
spinal cord into R. and L. sides
Spinal Cord / White Matter
• White matter is divided into columns;
Posterior Funiculus, Anterior Funiculus,
and Lateral Funiculus
Spinal Cord / White Matter
• Each column contains distinct bundles of
nerve axons called tracts
Spinal Cord / White Matter
Two Types of Tracts
1. Sensory (ascending) tracts – conduct
nerve impulses toward the brain
Spinal Cord / White Matter
2. Motor (descending) tracts – conduct
impulses down the cord
Connective Tissue Coverings of
Spinal Nerves
• A fiber is a single axon within an
endoneurium
Connective Tissue Coverings of
Spinal Nerves
• A fascicle is a bundle of fibers within a
perineurium
Connective Tissue Coverings of
Spinal Nerves
• A nerve is a bundle of fascicles within an
epineurium
Spinal Nerves and Nerve Plexus
• Each nerve divides into dorsal and
ventral rami
Spinal Nerves and Nerve Plexus
• Rami contains both motor and sensory
rami
Spinal Nerves and Nerve Plexus
• Dorsal rami – serve the skin and
musculture of the posterior body trunk at
their approximate level of emergence
Spinal Nerves and Nerve Plexus
• Ventral rami of spinal nerves T2 –T12 –
pass anteriorly to supply the muscles of
intercostal spaces, and the skin and
muscles of the anterior and lateral trunk
Spinal Nerves and Nerve Plexus
• Ventral rami of all other nerves – form
complex networks of nerves called
plexuses
Spinal Nerves and Nerve Plexus
• The plexuses diverge again to form
peripheral nerves
Spinal Nerves and Nerve Plexus
Four Plexuses
1. Cervical
2. Brachial
3. Lumbar
4. Sacral
Spinal Nerves and Nerve Plexus
1. Cervical Plexus
Supplies the skin and muscles of the head,
neck, and upper part of the shoulders
and diaphragm
Spinal Nerves and Nerve Plexus
• Damage to the spinal cord above the
origin of the phrenic nerves causes
respiratory arrest.
Spinal Nerves and Nerve Plexus
• Breathing stops because the phrenic
nerves stops sending impulses to the
diaphragm
Spinal Nerves and Nerve Plexus
2. Brachial Plexus
Supplies the upper extremities and a
number of neck and shoulder muscles
Spinal Nerves and Nerve Plexus
• In carpal tunnel syndrome there is damage
to the median nerve
Spinal Nerves and Nerve Plexus
3. Lumbar Plexus
Supplies the anterolateral abdominal wall,
external genitals, and part of the lower
extremities
Spinal Nerves and Nerve Plexus
• Femoral Nerve - Largest nerve arising
from the lumbar plexus
Spinal Nerves and Nerve Plexus
4. Sacral Plexus
Supplies the buttocks and part of the lower
extremities
Spinal Nerves and Nerve Plexus
• Sciatic Nerve – Largest nerve arising form
the sacral plexus
Spinal Nerves and Nerve Plexus
• Sciatica – Pain that extends from the
buttock down the back of the leg due to
injury to the sciatic nerve
Spinal Cord Physiology
• The white matter tracts are highways for
nerve impulse conduction to and from the
brain
Spinal Cord Physiology
• The gray matter receives and integrates
incoming and outgoing information
Spinal Cord Physiology / Sensory
Tracts
Sensory information from receptors travels
up the spinal cord via the;
1. Spinothalamic tracts
2. Posterior column tract
Spinal Cord Physiology / Sensory
Tracts
 Spinothalamic tracts carry pain, touch,
and temperature impulses
Spinal Cord Physiology / Sensory
Tracts
 Posterior columns carry proprioception
and vibration
Spinal Cord Physiology / Motor
Tracts
Motor info. travels from the brain down the
spinal cord to muscles and glands via
the;
1. Pyramidal tracts
2. Extrapyramidal tracts
Spinal Cord Physiology / Motor
Tracts
 Pyramidal tracts control voluntary,
purposeful motor movement of eyes,
mouth, face, arms, and legs
Spinal Cord Physiology / Motor
Tracts
 Extrapyramidal tracts control more
complex things like the accessory
adjustments we make to muscle tone to
adjust our posture
Spinal Cord Physiology / Reflexes
• The gray matter of the spinal cord serves
as an integrating center for spinal reflexes
Spinal Cord Physiology / Reflexes
• A reflex is a fast, predictable, automatic
response to changes in the environment
that helps to maintain homeostasis
Spinal Cord Physiology / Reflex Arc
Five functional components;
1. Receptor
2. Sensory Neuron
3. Motor Neuron
4. Integrating Center Neuron
5. Effector
Stretch Reflex
1. Slight stretching of a muscle stimulates
sensory receptors in the muscle called
muscle spindles
Stretch Reflex
2. In response to being stretched the
muscle spindle generates a nerve impulse
along a somatic sensory neuron and
enters the spinal cord via the posterior root
Stretch Reflex
3. In the integrating center of the spinal cord
the sensory neuron makes an excitatory
synapse with a motor neuron in the
anterior gray horn
Stretch Reflex
4. If the excitation is strong enough a nerve
impulse is propagated along the motor
neuron which extends from the spinal cord
to the muscle
Stretch Reflex
5. ACh is released at the NMJ which
triggers a muscle action potential in the
stretched muscle (effector) and the
muscle contracts